Apparatus for controlling cell transmission timing

ABSTRACT

In order to reduce a storage area for storing time information necessary to manage transmission timing of a plurality of cells in an asynchronous transfer mode type exchange, a shaper for use in the ATM exchange employs a plurality of cell transmission queues each having a different class. If there occurs a cell in a connection having a cell transmission rate R, one of the cell transmission queues is specified on the basis of the cell transmission rate R, wherein the cell is registered in one of a plurality of steps in the specified cell transmission queue in accordance with the quotient given using the cell transmission rate R.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for controlling celltransmission timing, for example, in an ATM (Asynchronous Transfer Mode)exchange.

2. Description of Prior Art

As one such exchange, Japanese patent laid-open publication No. 7-327033has taught a method and apparatus for controlling cell transmissiontiming. FIG. 7 depicts the configuration of the cell transmission timingcontroller (hereinafter, referred to as a shaper) disclosed in thepublication. The shaper accommodates a plurality of connections 7 eachinvolving a plurality of cells 8 to be transmitted. To control celltransmission, the shaper incorporates the cell interval managing unit 1,the cell transmission time managing unit 2, the cell multiplexing unit3, the connection managing unit 4, and the unit time generating unit 5,wherein the cell transmission time managing unit 2 includes the celltransmission time table 2A, the cell interval managing unit 1 includesthe cell interval table 1A, and the cell multiplexing unit 3 includesthe cell transmission scheduling table 3A. The cell transmission timetable 2A stores times at which cells are transmitted. The cell intervaltable 1A stores cell intervals between the times at which a cell(hereinafter, referred to as “preceding cell”) is transmitted and thetimes at which a cell following the preceding cell) (hereinafter,referred to as “following cell”) is transmitted.

To obtain the time at which the following cell will be transmitted, theshaper reads out of the cell interval table 2A a cell interval withrespect to the preceding cell and the following cell. Thereinafter, theshaper adds the read cell interval to the time at which the precedingcell will be transmitted or has been transmitted (hereinafter, referredto as a preceding cell transmission time), thus storing the precedingcell in the cell transmission time managing unit 2A. In this way, theshaper determines the time at which the following cell will betransmitted (hereinafter, referred to as a following cell transmissiontime.)

Here, a unit time [seconds/cell] is defined as the period of time whichone cell requires for transmission. Assuming that a cell transmissionrate of one of the connections 7 is R [cells/second] and that the celltransmission rate of the shaper is P [cells/second], the cell intervalin the connection is given as P/R [seconds/cell]. This indicates that asmaller cell transmission rate of a connection permits the cell intervalin the connection to be longer, and vice versa.

After reading out the following cell transmission time from the celltransmission time managing table 2A, the cell transmission time managingunit 2 registers the following cell in the cell transmission schedulingtable 3A in such a fashion that the following cell can be transmitted atthe following cell transmission time. Once the following celltransmission time comes, the following cell is permitted to betransmitted.

As described above, if the cell transmission rate of a connection 7 issmall, the cell interval in the connection 7 becomes large. Since thefollowing cell transmission time is calculated using the cell intervalwith respect the preceding cell and the following cell, the large cellinterval makes the following cell transmission time large. This forcesthe cell interval table 1A, the cell transmission time table 2A and thecell transmission scheduling table 3A to be large enough to store suchlarge values.

Herein, assuming that the cell transmission rate or bandwidth of theshaper is 622.08 [Megabits/second], namely, (622.08×10{circumflex over ()}6)/(8×53) [cells/second] and that the cell transmission rate R of aconnection 7 is 10 [cells/second], the cell transmission schedulingtable 3A requires a storage area corresponding to the cell interval morethan 146,717 [seconds/cell].

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide anapparatus for controlling cell transmission timing, which controls celltransmission in such a manner that a cell transmission rate of eachconnection to be controlled corresponds to a given transmission rate.

According to the present invention, an apparatus for controlling celltransmission timing, which determines following cell transmission timeof transmitting a following cell that follows a preceding cell, uses thepreceding cell transmission time of transmitting the preceding cell anda time interval specified by a cell transmission rate of a connectionalong which the preceding cell and the following cell flow, to registerthe following cell in a step so as to be transmitted at the followingcell transmission time. The apparatus comprises an accommodation circuitaccommodating a plurality of connections along which a plurality ofcells flow, each of the plurality of connections allocated a celltransmission rate that is represented with a cardinal number, anexponent, and a function of a mantissa. The apparatus also includes aplurality of cell transmission queues each being allocated a bandwidthfor transmitting the plurality of cells and temporarily storing theplurality of cells, each of the plurality of cell transmission queuesbeing referred to as a class and having a plurality of steps, each ofthe plurality of steps being a registered one of the plurality of thecells, the registered cells shifting toward a given step that permits acell shifted therein to be transmitted. The apparatus further includes acontrolling circuit controlling the registering of the cells in one ofthe plurality of steps in the plurality of queues, using the cardinalnumber, the exponent, and the function of the mantissa of the connectionof the cell.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of a shaper according to the presentinvention;

FIG. 2 shows steps in each of the cell transmission queues in the shaperof FIG. 1;

FIG. 3 shows a look-up table for use in retrieving a step suitable for acell;

FIG. 4 is a flowchart showing a procedure for calculating the step inthe first and second embodiments of the shaper;

FIG. 5 is a timing chart showing transmitting a following cell, FIG.5(A) of which shows a cell transmission in an ordinary case, FIG. 5(B)of which shows a cell transmission in a delay case, and FIG. 5(C) ofwhich shows a cell transmission in a recovery case;

FIG. 6 is a flowchart showing a procedure of calculating the step in thethird, fourth, and fifth embodiments of the shaper; and

FIG. 7 shows a configuration of a conventional apparatus for controllingcell transmission timing (shaper).

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Hereinafter, the preferred embodiments of the apparatus for controllingthe cell transmission timing (shaper) according to this invention willbe now described with reference to the accompanying drawings. The firstembodiment of the apparatus for controlling the cell transmission timingwill be explained referring to FIG. 1. The first embodiment featuresthat upon the occurrence of a cell in a connection, a step in a celltransmission queue in which the cell should be registered, is determinedon the basis of the cell transmission rate R of the connection. Morespecifically, when a cell occurs in a connection, the cell transmissionrate R of the connection is used to give the cell transmission intervalmantissa INCRE. Thereafter, the INCRE is used to give the stepdetermination factor QUOTIENT. Finally, the exponent e and mantissa m ofthe cell transmission rate R, and the step determination factor QUOTIENTare used to determine the step in which the cell should be registered.

Hereinafter, note that the term “cell” is often representative of theconnection in which the cell has occurred; for example, the cellregistered in a step represents the connection of the cell.

As shown in FIG. 1, the shaper 10 incorporates a plurality of celltransmission queue managing units 11-1˜11-n, a queue multiplex unit 12,a cell interval managing unit 13, a connection managing unit 14, a celltransmission time managing unit 15, and a unit time generator 16,wherein the shaper 10 accommodates a plurality of connections 19-1˜19-jthrough which a plurality of cells 30 pass.

The plurality of cell transmission queue managing units 11-1˜11˜ninclude a plurality of cell transmission queues 18-1˜18-n, respectively.Each of the plurality of cell transmission queues 18-1˜18-n has acorresponding bandwidth, wherein the bandwidth of the shaper 10 isexponentially divided into the plurality of the cell transmission queues18-1˜18-n. For example, assuming that the bandwidth of the shaper 10 is100 Mbps, the bandwidth of the cell transmission queue 18-1 is 0˜400Kbps, the bandwidth of the cell transmission queue 18-2 is 400˜1600Kbps, the bandwidth of the cell transmission queue 18-3 is 1600˜6400Kbps, the bandwidth of the cell transmission queue 18-4 is 6400Kbps˜25.6 Mbps, and the bandwidth of the cell transmission queue 18-5 is25.6˜100 Mbps. Each of the cell transmission queue managing units11-1˜11-n manages transmission timing of cells to be transmitted whichare registered in the corresponding one of the cell transmission queues18-1˜18-n.

As shown in FIG. 2, each of the cell transmission queues 18-1˜18-nincorporates a plurality of steps 40 which represent the order of thecells to be transmitted, wherein the head step Q0 indicates the placewhere a cell 30 laid therein is allowed to be transmitted and the othersteps where cells laid therein must wait for transmission. If a cellarises in one of the connections 19-1˜19-j, the cell experiencesexchanging in the shaper 10, more definitely in one of the celltransmission queues 11-1˜11-n, thus advancing to the respectivedestinations. Since each of the connections 19-1˜19-j has been given acell transmission rate R in advance, which is changeable with time, thecell transmission rate R serves to determine which of the celltransmission queues 18-1˜18-n the cell 30 should be assigned to, andwhich of steps 40 in the determined one of the cell transmission queues18-1˜18-n the cell 30 should be registered in. Registered cells in eachof the cell transmission queues 18-1˜18-n are shifted by one step, whichstep is equivalent to the respective unit time of cell transmissiondepending upon the cell transmission rates R of the respectiveconnections. After repeated shifting of the cells, if a cell reaches thehead step Q0, the cell is allowed to depart from the step Q0 fortransmission. In this way, the exchanging of the cell is completed.

Herein, the cell transmission rate R [cells/ second] will be describedin detail. The cell transmission rate R is expressed as a product of anexponent and a mantissa, more definitely, is approximated to be(b{circumflex over ( )}e)×f(m), where e denotes an exponent, m denotesmantissa (0≦m≦m_(max)), b denotes a cardinal number, and f(m) denotes amonotonically increasing function (1≦f(0)≦f(1)≦ . . .≦f(m)≦f(m_(max))<b). The maximum cell transmission rate R_(max) and theminimum cell transmission rate R_(min) are expressed by the expressions(1) and (2).

R_(max)=(b{circumflex over ( )}e_(max))×f(m′)  (1)

R_(min)=(b{circumflex over ( )}e_(min))×f(m″)  (2)

Herein, since e_(max) and e_(min) denote the maximum value and theminimum value of the exponent e, both of which have been fixed inadvance, if R_(max) or R_(min) is given, the corresponding f(m′) orf(m″) is given using the expression (1) or (2).

If m′≠m_(max), the expression (3) is satisfied, while if m′=m_(max), theexpression (4) is satisfied.

R_(max)=(b{circumflex over ( )}e_(max))×f(m′)≦P<(b{circumflex over ()}e_(max))×f(m′+1)  (3)

R_(min)=(b{circumflex over ( )}e_(max))×f(m_(max))≦P<(b{circumflex over( )}(e_(max)+1))×f(0)  (4)

where P denotes the fixed cell transmission rate [cells/second] of theshaper 10.

Returning to FIG. 1, the queue multiplex unit 12 controls a coincidenceamong transmission of cells that have reached the head step Q0 in eachof the cell transmission queues 18-1˜18-n, which permits one of them tobe outputted.

The cell interval managing unit 13 notifies the connection managing unit14 of a cell interval mantissa INCRE when there arises a cell to betransmitted in a connection, wherein the INCRE corresponds to themantissa m of the cell transmission rate R of the connection. The INCREis stored in the cell interval table 20. Since the cell transmissionrate R is changeable with time, the INCRE is similarly changeable withtime. The INCRE serves to determine the step 40 in which a cell shouldbe registered. The INCRE stored in the cell interval table 20 isavailable for the other processes because the processes can utilize theINCRE without repetitive calculation using the mantissa m. The INCREwill be described in detail later.

The connection managing unit 14 carries out various processes necessaryfor a variety of events such as initialization, cell occurrence, andcell transmission, for each connection. For example, for each cell 30 tobe transmitted, the connection managing unit 14 performs time managementfor cell transmission using the time counter 21, judges the celloccurrence and cell type, manages registration of the cell in a step 40of a cell transmission queue 18, and notifies the cell transmitting unit17 of information on the cell.

The time counter 21 develops by a specific time, which acts to select aportion of the current time NOW in accordance with each of the celltransmission rates R. The selected portion serves to manage shifting ofcells that are registered in a cell transmission queue 18-1˜18-n. Forexample, if a cell transmission rate R is large, the connection managingunit 14 selects a low order digit of the current time NOW, such as anano-second, while if a cell transmission rate R is small, it selects ahigh order bit of the current time NOW, such as a second. Using theselected portion of the current time NOW, and the cell interval mantissaINCRE, the connection managing unit 14 can determine the time at whicheach of the cells should be transmitted without any redundancy, moredefinitely, which of the steps 40 each of the cells should be registeredin. In summary, the connection managing unit 14 determines the precedingcell transmission time SENDTIME, using the selected portion of thecurrent time NOW.

The cell transmission time managing unit 15 stores the preceding celltransmission time SENDTIME in the cell transmission time table 22. Theunit time signal generator 16 generates some clock signals necessary formanagement of cell transmission.

Cell Transmission Interval Mantissa

Hereinafter, the cell transmission interval mantissa INCRE will be nowdescribed in detail. When the above expressions (1)˜(4) are satisfied,the cell transmission interval mantissa INCRE is defined by theexpressions (5) and (6), where k denotes an arbitrary value, and theINCRE is given through raising the decimals to a unit.

m≦m′: INCRE={R_(max)/f(m)}×k  (5)

m>m′: INCRE={R_(max)/f(m)}×k×b  (6)

When the expressions (5) and (6) are established, the expression (7) onthe cell transmission mantissa INCRE is established.

(b{circumflex over ( )}e_(max))×k≦INCRE<(b{circumflex over ()}(e_(max)+1))×k  (7)

Bandwidth Division and Allocation

Hereinafter, division of the bandwidth of the shaper 10 and allocationof the divided bandwidth to the plurality of cell transmission queues18-1˜18-n will be explained. As described above, the bandwidth of theshaper 10 is exponentially divided. The division is into a plurality ofsmall bandwidths by 1/(b{circumflex over ( )}w), where w denotes apositive integer. The small bandwidths are allocated to the plurality ofcell transmission queues 18-1˜18-n, respectively. Here, one of the celltransmission queues 18-1˜18-n that is allocated the largest bandwidth,is referred to as the class 0, another is allocated a bandwidth smallerthat the largest bandwidth is referred to as the class 1, and the othersare referred to likewise. As a result, the cell transmission queue 18that is allocated the smallest bandwidth is referred to as the classn_(max). All of the small bandwidths are represented by the followingexpressions (8-1)˜(8-7), where A=f(m′+1), B=f(m′), C=f(m″), b{circumflexover ( )}(e_(max)−(n_(max)+1)×w)×A(b{circumflex over ( )}e_(max))×C areestablished.

class 0: (b{circumflex over ( )}(e_(max)−w))×A<R0≦(b{circumflex over ()}(e_(max))×B  (8-1)

class 1: (b{circumflex over ( )}(e_(max)−2w))×A<R1≦(b{circumflex over ()}(e_(max)−w)×B  (8-2)

 class 2: (b{circumflex over ( )}(e_(max)−3w))×A<R2≦(b{circumflex over ()}(e_(max)−2w))×B  (8-3)

class n−1: (b{circumflex over ( )}(e_(max)−nw))×A<Rn−1≦(b{circumflexover ( )}(e_(max)−(n−1)w))×B  (8-4)

class n: (b{circumflex over ( )}(e_(max)−(n+1)w))×A<Rn≦(b{circumflexover ( )}(e_(max)−nw))×B  (8-5)

class (n_(max)−1): (b{circumflex over ()}(e_(max)−(n_(max])w))×A<Rn_(max)−1≦(b{circumflex over ()}(e_(max)−(n_(max)w))×B  (8-6)

class n_(max): (b{circumflex over ()}(e_(min)))×C<Rn_(max)≦(b{circumflex over ()}(e_(max)−(n_(max))w))×B  (8-7)

Each of the above bandwidths incorporates further a plurality ofcolumns. Herein, each of the columns are referred to as a sub-class. Forexample, assuming the class n involves a plurality of sub-classesSUBn(0)˜SUBn(w), the bandwidths Rn(0)˜Rn(w) of the sub-classes n(0)˜n(w)are defined as the expressions (9-1)˜(9-3).

(b{circumflex over ( )}(e_(max)−nw−1))×A<Rn0≦(b{circumflex over ()}(e_(max)−nw))×B  (9-1)

(b{circumflex over ( )}(e_(max)−nw−2))×A<Rn1≦(b{circumflex over ()}(e_(max)−nw−1))×B  (9-2)

(b{circumflex over ( )}(e_(max)−nw−w))×A<Rnw≦(b{circumflex over ()}(e_(max)−nw−w+1))×B  (9-3)

The above bandwidths Rn0˜Rnw correspond to the sub-classesSUBn(0)˜SUBn(w) in FIG. 3, respectively. In other word, assuming that b,w, and m are provided, in the case of class n, given e and m, one ofbandwidths Rn0˜Rnw is obtained, that is, one of the sub-classesSUBn(0)˜SUBn(w) is obtained.

Registration of Cell in Step

Registration of cells will be described, hereinafter. FIG. 3 shows alookup table for retrieving a step in which a cell 30 should beregistered. Provided that there arises a cell 30 in a connection 19, thecell transmission rate R, which is one of rates R0˜Rn_(max), specifiesthe one of the classes 0˜n_(max) to which the cell 30 should beassigned. In the class specified by the cell transmission rate R, one ofthe sub-classes in which the cell should be registered, for example, oneof the sub-classes SUBn(0)˜SUBn(w), is designated through the aboveprocedure. Further, given a step determination factor QUOTIENT, the step40 in which the cell 30 should be registered is retrieved, using thesub-class SUB and the step determination factor QUOTIENT over thelook-up table. After determination of the step 40, the cell 30 is setinto the step 40 of the cell transmission queue 18 corresponding to thestep 40 determined in the look-up table.

Shifting Cell

Hereinbelow, shifting registered cells will be described. The cells 30laid in the steps 40 are shifted to the respective neighboring stepstoward the head step Q0. For example, the cell in the step Q1 is shiftedto the step Q0, the cell in the step Q2 is shifted to the step Q1, andthe other cells in the other steps are shifted likewise. The frequencyof shifting in a cell transmission queues 18 depends upon the classthereof, and more specifically the frequency of shifting is inproportion with the cell transmission rate of the class. Therefore, forexample, the frequency of shifting in the cell transmission queue 18-1differs from that in the cell transmission queue 18-n. The shiftingoperation is indicated in detail by class in the following.

class 0: one time per unit time  (10-1)

class 1: one time per b{circumflex over ( )}w unit time  (10-2)

class 2: one time per b{circumflex over ( )}(w×2) unit time  (10-3)

class n-1: one time per b{circumflex over ( )}(w×(n−1)) unittime  (10-4)

class n: one time per b{circumflex over ( )}(w×n) unit time  (10-5)

class n_(max)−1: one time per b{circumflex over ( )}(w×(n_(max)−1)) unittime   (10-6)

class n_(max): one time per b{circumflex over ( )}(w×(n_(max))) unittime  (10-7)

Setting of Cell Transmission Timing

Hereinafter, the operation from cell occurrence to cell transmissionwill be described. First, the cell interval managing unit 13 determineswhich of the cell transmission queues 18-1˜18-n the cell 30 that hasoccurred in a connection 19 should be assigned to, and also which of thesteps 40 in the cell transmission queue 18 the cell should be registeredin, using cell transmission rate R of the connection 19. For example,when there arises a cell 30 in a connection 19-1, the cell transmissionrate R of the connection 19-1 serves to determine which of the celltransmission queues 18-1˜18-n the cell should be assigned to, andfurther, which of the steps in the determined one of the celltransmission queues 18-1˜18-n the cell should be registered. In case ofa first cell, however, the cell is registered in a head step, namely,the step Q0, whichever cell transmission queue 18 the cell 30 isassigned to. In most cases, a cell 30 is registered in a step other thanthe head step Q0. The cells registered in those steps in a celltransmission queue 18 shift toward the head step Q0. Once a cell reachesthe head step Q0, the cell is allowed to leave the cell transmissionqueue 18, namely, to be transmitted. If, for example, transmitting acell in a head step Q0 of a cell transmission queue 18-1 andtransmitting another cell in a head step Q0 of another cell transmissionqueue 18-2 are coincident with each other, the coincidence is adjusted,which permits the cells to be transmitted one by another.

When there occurs a following cell, which follows the first cell, in thesame connection 19-1, the connection managing unit 14 notifies the cellinterval managing unit 13 of the cell occurrence. The cell intervalmanaging unit 13 calculates the cell transmission interval mantissaINCRE, using the mantissa m of the cell transmission rate R of theconnection 19-1, thereby obtaining an addition SUM that is defined bythe expression (11).

SUM=T+INCRE  (11),

where the time counter T denotes the mantissa of the preceding celltransmission time SENDTIME.

Furthermore, the step determination factor QUOTIENT is obtained usingthe expression (12).

QUOTIENT=floor (SUM, (b{circumflex over ( )}e_(max))×k)  (12),

where the function “floor” gives the quotient of dividing the SUM by the((b{circumflex over ( )}e_(max))×k).

Thereafter, the time counter T experiences, an increment according tothe following expression (13).

T=SUM−QUOTIENT×((b{circumflex over ( )}e_(max))×k)  (13)

The new time counter T, which is rounded up or rounded down, will beused for obtaining the QUOTIENT when a further following cell occurs. Inaddition, the step determination factor QUOTIENT and the celltransmission interval mantissa INCRE satisfy the following expressions(14) and (15).

1≦QUOTIENT≦b  (14)

T<(b{circumflex over ( )}e_(max))x k≦INCRE<(b{circumflex over ()}(emax+1))×k  (15)

The cell interval managing unit 13 determines a cell transmission queue18 to which the cell 30 should be assigned, and a step 40 in which the40 cell should be registered, using the cell transmission rate R and thestep determination factor QUOTIENT, wherein the step 40 in which thecell 30 should be registered is determined pursuant to a rule asfollows.

(A) In a case in which b{circumflex over ()}{e_(max)−(w×n)−1}×f(m′+1)<R≦b{circumflex over ()}{(e_(max)−w×n)×f(m′)}:

If QUOTIENT=0, then register the cell in step Q0

If QUOTIENT=1, then register the cell in step Q1

If QUOTIENT=2, then register the cell in step Q2

. . .

If QUOTIENT=b, then register the cell in step Qb

(B) In a case in which

b{circumflex over ( )}{e_(max)−w×(n−2))×f(m′+1)}<R≦b{circumflex over ()}{(e_(max)−w×(n−1))×f(m′)}:

If QUOTIENT=0, then register the cell in step Q0

If QUOTIENT=1, then register the cell in step Qb

If QUOTIENT=2, then register the cell in step Q(b×2)

. . .

If QUOTIENT=b, then register the cell in step Q(b×b)

(C) In a case in which

b{circumflex over ( )}{e_(max)−w×(n−w))×f(m′+1)<R≦b{circumflex over ()}{(e_(max)−w×(n−w+1))×f(m′)}:

If QUOTIENT=0, then register the cell in step Q0

If QUOTIENT=1, then register the cell in step Q(b{circumflex over ()}(w−1)

If QUOTIENT=2, then register the cell in step Q(b{circumflex over ()}{(w−1)×2}

. . .

If QUOTIENT=b, then register the cell in step Q(b{circumflex over ()}{(w−1)×b}

As described above, in the first embodiment of the apparatus forcontrolling cell transmission timing, the bandwidth of the shaper 10 hasbeen exponentially divided into a plurality of small bandwidths, whileeach of the connections is allotted a cell transmission rate R, which isexpressed using an exponent e and a mantissa m. The small bandwidths areallocated to a plurality of the cell transmission queues 18-1˜18-n. Ineach of the cell transmission queues 18-1˜18-n a plurality of steps 40are involved, wherein only the cell 30 laid in the head step Q0 isallowed to be transmitted.

In summary, as shown in FIG. 4, if there occurs a cell 30 in aconnection 19 having a cell transmission rate R, the step 40 in the celltransmission queue 18 is determined using the cell transmission rate R.More specifically, the step 40 is determined using the exponent e-andthe mantissa m with reference to a look-up table shown in FIG. 3,wherein the exponent e serves to specify the class and the sub-classwhile the mantissa m serves to specify the step determination factorQUOTIENT. Thereafter, the step 40 is designated on the basis of thespecified class, sub-class, and QUOTIENT. Finally, the cell 30 isregistered in the designated step 40, and the cell transmission queue 18is specified by the class.

Since the cell transmission rate R of the connection and the bandwidthof the cell transmission queues 18 are defined in terms of exponent andmantissa, the storage area that stores the period of time used formanaging cell transmission can be reduced in comparison with theconventional art.

For example, assuming that the bandwidth of the shaper 10 is 622.08[Megabit/second], the bandwidth of a connection is 10[cell/second], thecardinal number b is 2, and w is 2, then the number of the classesbecomes nine and the number of the steps becomes five. The total numberf of steps becomes 45 (=5×9), which is enough to manage the celltransmission. Further, in contrast with the conventional art, if thebandwidth P of the shaper 10 becomes double, the total number of stepsincreases only to log₂ (P+1)/log₂ P, which facilitates expanding thecapacity of the shaper 10.

Further, the embodiment involves determining the time of transmitting acell using the cell transmission interval mantissa INCRE reduces tom′+1, pre-calculations employing real numbers necessary to obtain theINCRE.

Second Embodiment

Hereinafter, the second embodiment of the apparatus for controlling thecell transmission timing according to this invention will be described.The configuration and function of the second embodiment is similar tothose of the first embodiment, wherein the difference therebetween isthat another function of the cell interval managing unit 13 is added tothe second embodiment. More specifically, the additional function is tocontrol or manage a suspension and a delay of a following cell.

As shown in FIG. 5(A), in an ordinary case of the first embodiment,since the following cell occurs around the time to of transmitting thepreceding cell, the following cell can be transmitted at the time t2specified with both of the time t0 of the preceding cell transmissionand the time of period Tc, wherein the time of period Tc is defined asthe interval between the time of the ordinary preceding cell occurrenceand the ordinary following cell occurrence.

As shown in FIG. 5(B), however, if the following cell occurs at the time(t1′) at which a long period of time T1 elapses since the time t0, thefollowing cell is registered in such a manner that the following cellwill be transmitted at the time t3 specified with the time t1′ and theperiod of time Tc. Accordingly, the following cell fails to betransmitted at the time t2. As shown in FIG. 5(C), the second embodimentenables the delayed following cell to be transmitted at the time t2.

Hereinafter, the operation of the second embodiment will be explained indetail. In the second embodiment, when the cell interval managing unit13 obtains the time difference between the preceding cell transmissiontime SENDTIME denoting the time of transmitting the preceding cell andthe following cell transmission time THETIME denoting the time oftransmitting the following cell, to correct the time of transmitting thefollowing cell.

More definitely, first, the cell interval managing unit 13 obtains thetime difference T1 between the time t0 and the time t1′. Next, itdivides the time difference T1 by the unit time b{circumflex over ()}(e_(max)−e), thus converting the time difference T1 into the number ofsteps (t1′−t0)/(b{circumflex over ( )}(e_(max)−e)). Finally, itsubtracts the number of steps (t1′−t0)/(b{circumflex over ()}(e_(max)−e)) from the step determination factor QUOTIENT, therebydetermining the step 40 in which the following cell should be actuallyregistered. In this way, the step determination factor QUOTIENT isadjusted. This procedure is defined by the expressions (16) and (17).

if m≦m′, then QUOTIENT=max (0,{QUOTIENT−(THETIME−SENDTIME)/(b{circumflex over ( )}(e_(max)−e))})  (16)

 if m>m′, then QUOTIENT=max (0,{QUOTIENT−(THETIME−SENDTIME)/(b{circumflex over ()}(e_(max)−e−1))})  (17)

For example, assuming that the time difference T1 is two time units andthe original step determination factor QUOTIENT Tc is given as threetime units, the step determination factor QUOTIENT is corrected to onetime unit, which permits the following cell to be registered in the step40 corresponding to the corrected step determination factor QUOTIENT,one unit time.

As described above, in accordance with the second embodiment, even ifthe occurrence of the following cell is delayed, the following cell canbe registered so as to be transmitted at the time at which the followingcell must be transmitted primarily.

Third to Fifth Embodiments

Hereinbelow, the third to fifth embodiments will be now described. Priorto detailing those embodiments, outlines thereof will be explainedreferring to FIG. 6.

In comparison with the above-described first and second embodiments, allof the following embodiments feature extracting or selecting a portionfrom the current time for each of the connections 19, namely, for eachof the cell transmission queues 18. This has been already discussed inthe explanation of the time counter 21. Such a function leads to savingor reducing storage area for storing information with respect to time.In addition to this feature, the embodiments have respective featuresdiscussed below.

As shown in FIG. 6, the embodiments involve several calculations, suchas calculating the cell transmission interval mantissa INCRE using themantissa m of the cell transmission rate R, calculating the class andthe sub-class, and calculating the time SENDTIME and the time NOWTIME,which NOWTIME will be exactly defined later.

The functions of the embodiments are as following.

(1) Third embodiment

(1-1) Initialization

Storing SENDTIME: (A)→(B)→(D)→(E)

(1-2) Change in cell transmission

Storing SENDTIME: (A)→(B)→(D)→(E)

(1-3) Occurrence of cell

Determining QUOTIENT: {(A)→(F)→(H)→(I)} and {(A)→(B)→(D)→(J)}

Determining step: {(A)→(B)→(K)} and {(A)→(C)→(L)}

(1-4) After cell transmission

Storing SENDTIME: (A)→(B)→(D)→(E)

(2) Fourth embodiment

(2-1) Initialization

Storing SENDTIME: (A)→(B)→(D)→(E)

(2-2) Change in cell transmission

Storing SENDTIME: (A)→(B)→(D)→(E)

(2-3) Occurrence of cell

Determining QUOTIENT: (A)→(B)→(D)→(J)

Determining step: {(A)→(B)→(K)} and {(A)→(C)→(L)}

(2-4) After cell transmission

Storing SENDTIME: (A)→(B)→(D)→(E)

Precalculating for QUOTIENT: (A)→(F)→(H)→(I)

(3) Fifth embodiment

(3-1) Initialization

Storing class: (A)→(B)

Storing sub-class: (A)→(C)

Storing SENDTIME: {(A)→(B)}→(D)→(E)

(3-2) Change in cell transmission

Storing class: (A)→(B)

Storing sub-class: (A)→(C)

Storing SENDTIME: {(A)→(B)}→(D)→(E)

(3-3) Occurrence of cell

Determining QUOTIENT: (D)→(J)

Determining step: {(B)→(K)} and {(C)→(L)}

(3-4) After cell transmission

Storing SENDTIME: (D)→(E)

Precalculating for QUOTIENT: (H)→(I)

As shown above, in the third embodiment, calculating the celltransmission interval INCRE (F) is implemented at the occurrence of acell (1-3). On the contrary, in the fourth embodiment, the calculation(F) is performed after transmission of a cell (2-4). In the fifthembodiment, the class (B) and the sub-class (C), which are calculated atinitialization and upon changing the cell transmission rate R, arestored thereat (3-1) and (3-2) so as to be available for subsequentcalculations such as calculating the time NOWTIME, and calculating thetime SENDTIME, in contrast with the third and fourth embodiments wherethe class and the sub-class are calculated but not stored.

Third Embodiment

Hereinafter, the third embodiment of the apparatus for controlling thecell transmission timing will be now described. The third embodimentfeatures extracting or selecting a portion from the current time. Theextraction or selection depends upon the connections 19, moredefinitely, the cell transmission rate R. The reason for such filteringor screening is as follows.

The step determination factor QUOTIENT is given on the basis of thecurrent time, namely, the time of the following occurrence. Herein, theinformation denoting the current time includes much information, such assecond information, millisecond information, and nanosecond information.However, obtaining a step determination factor QUOTIENT does not requireall of that information; determination of the QUOTIENT depends upon thecell transmission rate as does the determination of the class.

Hereinbelow, the present time or current time is referred to as thecurrent time NOW, which is approximately equivalent to the time THETIMEin the first and second embodiments. Also, the portion extracted orselected from the current time NOW is referred to as the following celltransmission time NOWTIME, wherein the time NOWTIME depends upon theclass, namely, the cell transmission rate R. The SENDTIME is the same asthat in the first and second embodiments.

Determination of Step

The connection managing unit 14 determines in which of the steps 40 acell 30 to be transmitted should be registered, that is to say, a stepdetermination factor QUOTIENT. The determination is carried out usingthe time NOWTIME. Herein, the time NOWTIME is defined using the time NOWand each of the bandwidths of the cell transmission queues 18-1˜18-n.The time NOWTIME is expressed as follows.

class 0: NOWTIME=NOW

class 1: NOWTIME=NOW/b{circumflex over ( )}w

class 2: NOWTIME=NOW/b{circumflex over ( )}2w

class n-1: NOWTIME=NOW/b{circumflex over ( )}(n−1)w

class n: NOWTIME=NOW/b{circumflex over ( )}nw

class n_(max)-1: NOWTIME=NOW/b{circumflex over ( )}(n_(max)−1)w

class n_(max): NOWTIME=NOW/b{circumflex over ( )}(n_(max))w

Operation

Hereinbelow, the operation of the third embodiment will be described.First, if there arises a cell 30 in a connection 19, the connectionmanaging unit 14 obtains the exponent e and the mantissa m from the celltransmission rate R of the connection 19. Next, it determines to whichof the cell transmission queues 18 the cell 30 should be assigned, usingthe exponent e, which gives a class. Thereafter, it extracts a portionof the current time NOW in accordance with the class of the obtainedcell transmission queue 18, thereby setting the extracted portion as thetime NOWTIME.

Initialization

The connection manage 14 notifies the cell transmission time managingunit 15 of the time NOWTIME. The cell transmission time managing unit 15stores the time NOWTIME in the cell transmission time table 22, as thetime SENDTIME denoting the time at which the preceding cell has beentransmitted. Simultaneously, the cell transmission time managing unit 14defaults the step determination factor QUOTIENT, that is, sets it tozero.

Change in Cell Transmission Rate

If the cell transmission rate of the connection 19 changes from R to R′,the following operation is performed. First, the connection managingunit 14 obtains the new exponent e and the new mantissa m from the newcell transmission rate R′. Next, it selects a portion of the currenttime NOW in accordance with the class of the above cell transmissionqueue 18, thus obtaining the time NOWTIME. Further, the connectionmanaging unit 14 notifies the cell transmission time managing unit 15 ofthe time NOWTIME. The cell transmission time managing unit 15 stores thetime NOWTIME in the cell transmission time table 22 as the timeSENDTIME.

Occurrence of Cell to be Transmitted

If there occurs a cell 30 to be transmitted in a connection, theconnection managing unit 14 obtains the addition SUM of the time counterT and the cell transmission interval mantissa INCRE. Thereafter, theconnection managing unit 14 divides the addition SUM by (b{circumflexover ( )}e_(max))×k to obtain a quotient, thus setting the quotient asthe step determination factor QUOTIENT. Simultaneously, the connectionmanaging unit 14 develops the time counter T, using the remainder. Thisprocessing advances pursuant to the above expressions (11)˜(15).

Using the time SENDTIME and the time NOWTIME, the connection managingunit 14 implements the expressions (18) and (19), thereby determiningthe step determination factor QUOTIENT.

If m≦m′, QUOTIENT=max (0, QUOTIENT−(NOWTIME—SENDTIME))  (18)

If m>m′, QUOTIENT=max (0, QUOTIENT−(NOWTIME−SENDTIME)  (19)

Subsequently, the connection managing unit 14 determines the step 40based upon the QUOTIENT, the class, and the sub-class, therebyregistering the cell 30 in the step 40. The registered cell is shiftedtoward the head step Q0 by one unit time; once the cell 30 reaches thehead step Q0, the cell 30 is permitted to be transmitted.

Operation After Cell Transmission

After cell transmission, the connection managing unit 14 extracts aportion of the current time NOW in accordance with the cell transmissionrate of the connection to obtain the time NOWTIME, whereby theconnection managing unit 14 notifies the cell transmission time managingunit 15 of the obtained NOWTIME. Thereafter, the cell transmission timemanaging unit 15 stores the NOWTIME in the cell transmission time table22 as the SENDTIME. In this way, the NOWTIME for the preceding cell willbe available as the SENDTIME for the following cell.

As described above, the third embodiment obtains the time NOWTIME byextracting a portion from the time NOW on the basis of the celltransmission rate R of the connection 19. Hence the storage area forstoring time information necessary to calculate the QUOTIENT is reduced.

Fourth Embodiment

Hereinafter, the fourth embodiment of the apparatus for controlling thecell transmission timing according to this invention will be described.The configuration and function of the fourth embodiment are almost thesame as those of the third embodiment, whereas the function of the cellinterval managing unit 13 in this embodiment differs from that in thethird embodiment. More specifically, the cell interval manger 13 of theembodiment notifies the connection managing unit 14 of the celltransmission interval mantissa INCRE corresponding to the mantissa m ofthe cell transmission rate of the connection, after cell transmission inlieu of at cell occurrence in the third embodiment. This enablesdispersing processes for a plurality of cells that have occurredsimultaneously.

The differences between the fourth embodiment and the third embodiment,are in the operation at cell occurrence and the operation after celltransmission. Hereinbelow, therefore those operations will be described.

Operation at Cell Occurrence

If there arises a cell 30 in a connection 19, the cell transmission timemanaging unit 15 reads out the SENDTIME regarding the connection 19 fromthe cell transmission time table 22, to the connection managing unit 14.The connection managing unit 14 implements the expressions (20) and (21)using the NOWTIME and the SENDTIME, thereby obtaining the stepdetermination factor QUOTIENT.

If m≦m′, QUOTIENT=max (0, QUOTIENT−(NOWTIME−SENDTIME))  (20)

If m>m′, QUOTIENT=max (0, QUOTIENT−(NOWTIME−SENDTIME))  (21)

The other functions are the same as those of the third embodiment.

Operation After Cell Transmission

After cell transmission, the connection managing unit 14 extracts aportion of the time NOW according to the cell transmission rate of theconnection to obtain the time NOWTIME, and notifies the celltransmission time managing unit 15 of the same. The cell transmissiontime managing unit 15 stores the time NOWTIME in the cell transmissiontime table 22 as the time SENDTIME. At this time, the connectionmanaging unit 14 calculates the addition SUM of the time counter T andthe cell transmission interval mantissa INCRE. Further, the connectionmanaging unit 14 divides the SUM by (b{circumflex over ( )}e_(max))×k toobtain the step determination factor QUOTIENT. Also, it develops thetime counter T using the remainder. Those values are indicated by theexpressions (11)˜(15).

As described above, according to the fourth embodiment, preparation forvalues necessary to obtain the step determination factor QUOTIENT iscarried out after cell transmission. Therefore, even if a plurality ofcells occur simultaneously, the preparation for values necessary toobtain the respective QUOTIENTS does not need to be performed at thecell transmission, thereby avoiding concentration of those processes.

Fifth Embodiment

The configuration and function of the fifth embodiment is roughlysimilar to the those of the third and fourth embodiments. The fifthembodiment features the operations of the connection managing unit 14and the cell interval managing unit 13. More definitely, in the fifthembodiment, storing the class and the sub-class are performed atinitialization and at changing in the cell transmission rate R. Theclass and the sub-class are available for processes that follow such astoring. For example, when extracting a portion of the time NOW toobtain the time NOWTIME, the connection managing unit 14 uses the class.When registering the cell in a step, the connection managing unit 14uses the sub-class.

Since preparation for values to give a step determination factorQUOTIENT requires the cell interval mantissa INCRE according to themantissa m of the cell transmission rate R, the cell interval managingunit 13 notifies the connection managing unit 14 of the INCRE, aftercell transmission and at cell occurrence.

Initialization

Assuming that the cell transmission rate of one connection 19 is R1,upon initialization for the connection 19, the connection managing unit14 stores the class and the sub-class given using the exponent e1 andthe mantissa m1 of the cell transmission rate R1. On the other hand, theconnection managing unit 14 extracts a part of the current time NOWcorresponding to the class to obtain the time NOWTIME, thus notifyingthe cell transmission time managing unit 15 of the same. The celltransmission time managing unit 15 stores the time NOWTIME in the celltransmission time table 22 as the time SENDTIME. Simultaneously, theconnection managing unit 14 obtains the cell transmission intervalmantissa INCRE from the mantissa m1 of the cell transmission rate R1 ofthe connection 19, which is stored in the cell interval table 22 by thecell interval managing unit 13. Further, the connection managing unit 14defaults the step determination factor QUOTIENT, namely, sets it tozero. To summarize, the initialization permits the class and thesub-class to be stored as well as the time SENDTIME.

Change in Cell Transmission Rate

If the cell transmission rate of the connection 19 changes from R1 toR2, the connection managing unit 14 stores the class and the sub-classgiven using the exponent e2 and the mantissa m2 of the cell transmissionrate R2. Moreover, the connection managing unit 14 selects a portion ofthe current time NOW to obtain the time NOWTIME, thus notifying the celltransmission time managing unit 15 of the time NOWTIME. The celltransmission time managing unit 15 stores the time NOWTIME in the celltransmission time table 22 as the time SENDTIME. At this time, theconnection managing unit 14 obtains the cell transmission intervalmantissa INCRE from the mantissa m2 of the cell transmission rate R2 ofthe connection 19, whereby the cell interval managing unit 13 stores thetransmission interval mantissa INCRE in the cell interval table 22. Insummary, changing the cell transmission rate allows the class and thesub-class to be stored as well as the time SENDTIME, similarly to theinitialization.

Operation at Cell Occurrence

The connection managing unit 14 obtains the addition SUM of the timecounter T and the cell transmission interval mantissa INCRE, and dividesthe addition SUM by the (b{circumflex over ( )}e_(max))×k in order toobtain the step determination factor QUOTIENT. Thereafter, theconnection managing unit 14 updates the time counter T using theremainder. Those values are shown by the expressions (11)˜(15).

The connection managing unit 14 implements the expressions (11) and(12), using the time SENDTIME and the time NOWTIME, thus determining thestep determination factor QUOTIENT. Thereafter, the connection managingunit 14 determines the step on the basis of the step determinationfactor QUOTIENT, the class, and the sub-class to register the celltherein. Cells registered in such a way are shifted toward to the headstep Q0, whereby the cell that arrives thereat is permitted to betransmitted.

Operation After Cell Transmission

The connection managing unit 14 extracts a portion of the current timeNOW corresponding to the cell transmission rate R of the connection,thereby generating the time NOWTIME to notify the cell transmission timemanaging unit 15 of the same. The cell transmission time managing unit15 stores the time NOWTIME in the cell transmission time table 22 as thetime SENDTIME.

At this time, the connection managing unit 14 obtains the addition SUMof the time counter T and the cell transmission interval mantissa INCREto divide it by (b{circumflex over ( )}e_(max))×k, thus setting thequotient of the division as the step determination factor QUOTIENT. Thevalues are indicated by the expressions (11)˜(15).

As described above, in accordance with the fifth embodiment, both of theclass and the sub-class are stored at the initialization and thechanging the cell transmission rate. Therefore, a step determinationfactor QUOTIENT can be obtained without repetitive calculation of theclass and the sub-class, which leads to reduction of calculation time.

Other Embodiment

The above embodiments employs the expressions (5), (6), (12), and (13)in order to obtain the cell transmission interval mantissa INCRE.However, in lieu of the expressions (5) and (6), the followingexpression may be available.

INCRE=(R_(max)/f(m))×k  (22)

Also, in lieu of the expressions (12) and (13), the followingexpressions (23)˜(26) may be available.

If m≦m′, QUOTIENT=floor (SUM, (b{circumflex over ( )}e_(max))×k)  (23)

T=SUM−QUOTIENT×((b{circumflex over ( )}e_(max))×k)  (24)

If m>m′, QUOTIENT=floor (SUM, (b{circumflex over ()}(e_(max)−1))×k)  (25)

T=SUM−QUOTIENT×(b{circumflex over ( )}(e_(max)−1)×k)  (26)

While the present invention has been disclosed in terms of the preferredembodiment in order to facilitate a better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

What is claimed is:
 1. An apparatus for controlling cell transmission timing, which determines a following cell transmission time of transmitting a following cell that follows a preceding cell, using a preceding cell transmission time of transmitting the preceding cell and a time interval specified by a cell transmission rate of a connection along which the preceding cell and the following cell flow, to register the following cell in a step so as to be transmitted at the following cell transmission time, the apparatus for controlling cell transmission timing comprising: an accommodation circuit accommodating a plurality of connections along which a plurality of cells flow, each of the plurality of connections being allocated a cell transmission rate represented with a cardinal number, an exponent, and a function of a mantissa; a plurality of cell transmission queues, each being allocated a bandwidth for transmitting the plurality of cells and temporarily storing the plurality of cells, each of the plurality of cell transmission queues having a plurality of steps, each of the plurality of steps having registered therein one cell among the plurality of the cells, registered cells shifting toward a given step thereby permitting a cell shifted therein to be transmitted; and a managing circuit controlling registering of the one cell in one of the plurality of steps in the plurality of queues, using the cardinal number, the exponent, and the function of the mantissa of the connection of the one cell.
 2. An apparatus for controlling cell transmission timing, which determines a following cell transmission time of transmitting a following cell that follows a preceding cell, using a preceding cell transmission time of transmitting the preceding cell and a time interval specified by a cell transmission rate of a connection along which the preceding cell and the following cell flow, to register the following cell in a step so as to be transmitted at the following cell transmission time, the apparatus for controlling cell transmission timing comprising: an accommodation circuit accommodating a plurality of connections along which a plurality of cells flow, each of the plurality of connections being allocated a cell transmission rate represented with a cardinal number, an exponent, and a function of a mantissa; an interval circuit calculating the time interval using the function of the mantissa of the cell transmission rate allocated to the connection; a plurality of cell transmission queues, each being exponentially allocated a bandwidth for transmitting the plurality of cells and temporarily storing the plurality of cells, each of the plurality of cell transmission queues being identified by a class and having a plurality of steps, each of the plurality of steps having registered therein one cell among the plurality of the cells, registered cells shifting toward a given step thereby permitting a cell shifted therein to be transmitted; a class circuit calculating a class of a cell transmission queue in which a cell is registered, using the exponent; a sub-class circuit calculating a sub-class in a class, using the exponent; a quotient circuit calculating a quotient using the preceding cell transmission time of transmitting the preceding cell, the time interval, the cardinal number, and the exponent; a look-up table used for retrieving a step in which the cell is registered; a time circuit updating the preceding cell transmission time of transmitting the preceding cell; a step circuit determining a step from the look-up table, using the class, the sub-class, and the quotient; and a registration circuit registering the cell in the determined step.
 3. An apparatus for controlling cell transmission timing as set forth in claim 2, further comprising a circuit obtaining a delay time between the preceding cell transmission time of transmitting the preceding cell and the time of occurrence of the following cell, wherein the quotient circuit corrects the quotient using the delay time, and the step circuit determines the step on the basis of the corrected quotient.
 4. An apparatus for controlling cell transmission timing as set forth in claim 3, further comprising a first extraction circuit extracting a first information portion from information denoting the preceding cell transmission time of transmitting the preceding cell, in accordance with the cell transmission rate of the connection; and a second extraction circuit extracting a second information portion from information denoting the time of occurrence of the following cell, in accordance with the cell transmission rate of the connection, wherein the step circuit corrects the quotient using the first information portion and the second information portion.
 5. An apparatus for controlling cell transmission timing as set forth in claim 4, wherein the calculation by the interval circuit and the updating by the time circuit are implemented at the occurrence of the following cell.
 6. An apparatus for controlling cell transmission timing as set forth in claim 4, wherein the calculation by the interval circuit and the updating by the time circuit are implemented after transmission of the preceding cell.
 7. An apparatus for controlling cell transmission timing as set forth in claim 4, wherein the calculation by the class circuit and the calculation by the sub-class circuit are implemented upon an initialization of controlling cell transmission timing, and are stored to be available for the calculation by the quotient circuit.
 8. An apparatus for controlling cell transmission timing as set forth in claim 4, wherein the calculation by the class circuit and the calculation by the sub-class circuit are implemented upon a change in cell transmission rate, and are stored to be available for the calculation by the quotient circuit.
 9. An apparatus for controlling cell transmission timing, which controls cell transmission in such a manner that a cell transmission rate of each of a plurality of connections to be controlled corresponds to a given transmission rate, the apparatus for controlling cell transmission timing comprising: a plurality of queues each corresponding to a plurality of transmission frequency bands; queue management means for shifting a one of the connections positioned at each of a plurality of steps constituting the queues with frequency corresponding to the transmission rate, and for transmitting a cell transmission request from a connection positioned in the head of the steps in turn; cell transmission management means for determining to which transmission rate each connection belongs, and for determining at which of the steps corresponding to the transmission band the connection is positioned, based upon a cell transmission rate given by a mantissa and a following cell transmission request target value given by a time counter value corresponding to the mantissa, the cell transmission rate for each connection being expressed using an exponent and a mantissa; and cell transmission means for transmitting a cell for a connection that receives a cell transmission request from one of the plurality of queues.
 10. An apparatus for controlling cell transmission timing as set forth in claim 9, wherein the cell interval management means obtains a cell transmission interval mantissa corresponding to each connections from among a plurality of cell transmission interval mantissas calculated on all of the mantissas in advance.
 11. An apparatus for controlling cell transmission timing as set forth in claim 9, wherein the cell interval management means converts, for each queue, an elapsed time after transmission of a preceding cell into a number of steps for each queue, and advances by said number of steps the position of the step in which the connection is positioned from the position of the step determined based upon the following cell transmission request target value, in determining in which of the steps in the queues the connection is positioned.
 12. An apparatus for controlling cell transmission timing as set forth in claim 9, wherein the queue management means carries out shifting of connections in the steps with frequency corresponding to the transmission band corresponding to the queue on the basis of link information as to the number of connections that the queue corresponding to each of the plurality of transmission bands is capable of accommodating and first and last connection information on each of the steps for each queue.
 13. An apparatus for controlling cell transmission timing, which manages cell transmission timing on the basis of a transmission queue corresponding to a transmission band to which a cell transmission rate belongs, a plurality of transmission queues corresponding to each of the bands big defined through exponential division of the transmission band, the apparatus for controlling cell transmission timing comprising: transmission queue management means for shifting each connection registered in each step of each transmission queue at time intervals corresponding to said each transmission queue and outputs a cell transmission request according to said each transmission queue upon arrival at a head step; following cell transmission time calculation means for filtering a current time controlled by a system in initializing connections and/or in updating cell transmission rates in accordance with the cell transmission rate for each connection, and storing a transmission time corresponding to the cell transmission rate as a transmission time of a preceding cell; means for obtaining a cell transmission interval mantissa giving a transmission interval of the connection and a following cell transmission request target value related to the connection from a time counter value corresponding to the cell transmission interval mantissa and obtaining a temporal value of a step determination factor used for specifying a position of the step in the transmission queue in which the connection is registered on the basis of the target value upon occurrence of a cell; means for finally determining a step determination factor by calculating a difference between the transmission time of the preceding cell and the transmission time calculated through filtering the current time controlled by the system, to take into consideration a time that elapses before occurrence of a new cell after transmission of the preceding cell; connection registration means for registering each connection in a given step position on the corresponding transmission queue on the basis of the finally determined step determination factor; and cell transmission means, responsive to a cell transmission request transmitted from a transmission queue, for transmitting a cell of a connection corresponding to the cell transmission request via a transmission path.
 14. An apparatus for controlling cell transmission timing, which manages cell transmission timing on the basis of a transmission queue corresponding to a transmission band to which a cell transmission rate belongs, a plurality of transmission queues corresponding to each of the bands being defined through exponential division of the transmission band, the apparatus for controlling cell transmission timing comprising: transmission queue management means for shifting each connection registered in each step of each transmission queue at time intervals corresponding to said each transmission queue and outputs a cell transmission request according to said each transmission queue upon arrival at a head step; following cell transmission time calculation means for filtering a current time controlled by a system in initialing connections and/or in updating cell transmission rates in accordance with the cell transmission rate for each connection, and storing a transmission time corresponding to the cell transmission rate as a transmission time of a preceding cell; means for obtaining a cell transmission interval mantissa giving a transmission interval of the connection and a following cell transmission request target value related to the connection from a time counter value corresponding to the cell transmission interval mantissa and obtaining a temporal value of a step determination factor used for specifying a position of the step in the transmission queue in which the connection is registered on the basis of the target value after transmission of a cell; means for finally determining a step determination factor by calculating a difference between a transmission time of the preceding cell and the transmission time calculated through filtering the current time controlled by the system, to take into consideration a time that elapses before occurrence of a new cell after the transmission of the preceding cell upon occurrence of a cell; connection registration means for registering each connection in a given step position on the corresponding transmission queue on the basis of the finally determined step determination factor; and cell transmission means, responsive to a cell transmission request transmitted from a transmission queue, for transmitting a cell of a connection corresponding to the cell transmission request via a transmission path.
 15. An apparatus for controlling cell transmission timing, which manages cell transmission timing on the basis of a transmission queue corresponding to a transmission band to which a cell transmission rate belongs, a plurality of transmission queues corresponding to each of the bands being defined through exponential division of the transmission band, the apparatus for controlling cell transmission timing comprising: transmission queue management means for shifting each connection registered in each step of each transmission queue at time intervals corresponding to said each transmission queue and outputs a cell transmission request according to said each transmission queue upon arrival at a head step; class and sub-class determining means for obtaining and storing a transmission queue corresponding to the cell transmission rate of the connection, a class, and a sub-class, which specify a transmission bandwidth thereof upon initialization of a connection and/or upon updating a cell transmission rate; means for obtaining a mantissa of a step determination factor used for specifying a step position in a queue in which the connection is registered and for determining a transmission queue and a step position finally with reference to the class and the sub-class obtained and stored by the class and sub-class determining means upon initializing the connection and/or updating the cell transmission rate in determining the transmission queue and the step position of the queue in which the connection is registered; connection registration means for registering each connection in a given step position on the corresponding transmission queue on the basis of determination by the step determination determining means; and cell transmission means, responsive to a cell transmission request transmitted from a transmission queue, for transmitting a cell of a connection corresponding to the cell transmission request via a transmission path. 